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Abstract:

A membrane electrode assembly including an electrolyte membrane; a
catalyst layer on the electrolyte membrane; a gas diffusion layer
attached to the catalyst layer; and an adhesive layer between the
electrolyte membrane and the gas diffusion layer around an outer edge of
the catalyst layer, and a fuel cell stack including a plurality of unit
cells, each including one of the membrane electrode assemblies.

Claims:

1. A membrane electrode assembly comprising: an electrolyte membrane; a
catalyst layer on the electrolyte membrane; a gas diffusion layer
attached to the catalyst layer; and an adhesive layer between the
electrolyte membrane and the gas diffusion layer around an outer edge of
the catalyst layer.

2. The membrane electrode assembly of claim 1, wherein the adhesive layer
is on at least one of the electrolyte membrane or the gas diffusion layer
facing each other, and bonds the electrolyte membrane and the gas
diffusion layer to each other.

3. The membrane electrode assembly of claim 1, wherein an inner edge of
the adhesive layer is spaced apart from the outer edge of the catalyst
layer.

4. The membrane electrode assembly of claim 1, wherein the adhesive layer
is arranged as a closed curved line around the outer edge of the catalyst
layer.

5. The membrane electrode assembly of claim 1, further comprising an edge
protection layer on an outer portion of the electrolyte membrane along
the outer edge of the catalyst layer.

6. The membrane electrode assembly of claim 5, wherein the adhesive layer
is on at least one of the edge protection layer or the gas diffusion
layer facing each other, and bonds the edge protection layer and the gas
diffusion layer to each other.

7. The membrane electrode assembly of claim 6, wherein an inner edge of
the adhesive layer is spaced apart from a boundary line between the edge
protection layer and the catalyst layer.

8. The membrane electrode assembly of claim 5, wherein the adhesive layer
is arranged as a closed curved line along the edge protection layer.

9. The membrane electrode assembly of claim 1, wherein the adhesive layer
is heat-treated in a vacuum or atmosphere.

11. The membrane electrode assembly of claim 1, wherein the adhesive
layer comprises at least one of epoxy, urethane, silicon, or acryl.

12. A fuel cell stack comprising: a plurality of unit cells, each
comprising a membrane electrode assembly and separators attached to both
sides of the membrane electrode assembly, respectively; and a pressure
plate supporting and applying pressure to the plurality of unit cells,
wherein the membrane electrode assembly comprises: an electrolyte
membrane; a catalyst layer on the electrolyte membrane; a gas diffusion
layer attached to the catalyst layer; and an adhesive layer between the
electrolyte membrane and the gas diffusion layer around an outer edge of
the catalyst layer.

13. The fuel cell stack of claim 12, wherein the adhesive layer is on at
least one of the electrolyte membrane or the gas diffusion layer, and
bonds the electrolyte membrane and the gas diffusion layer to each other.

14. The fuel cell stack of claim 12, further comprising an edge
protection layer on an outer portion of the electrolyte membrane along
the outer edge of the catalyst layer.

15. The fuel cell stack of claim 14, wherein the adhesive layer is on at
least one of the edge protection layer or the gas diffusion layer facing
each other, and bonds the edge protection layer and the gas diffusion
layer to each other.

Description:

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to and the benefit of Korean
Patent Application No. 10-2011-0093664, filed on Sep. 16, 2011 in the
Korean Intellectual Property Office, the entire content of which is
incorporated herein by reference.

BACKGROUND

[0002] 1. Field

[0003] Aspects of embodiments of the present invention relate to a
membrane electrode assembly and a fuel cell stack.

[0004] 2. Description of the Related Art

[0005] As known in the related art, a fuel cell is configured to convert
chemical reaction energy of hydrogen contained in hydrogen oxide-based
fuel and oxygen contained in an oxidizing agent into electrical energy.

[0006] Such a fuel cell may be generally categorized as a polymer
electrolyte membrane fuel cell or a direct oxidation fuel cell.

[0007] The polymer electrolyte membrane fuel cell is configured as a fuel
cell body, or stack, and has a structure that generates electrical energy
through an electrochemical reaction between hydrogen supplied from a
reformer and an oxidizing agent supplied by the activation of an air pump
or a fan.

[0008] Unlike the polymer electrolyte fuel cell, the direct oxidation fuel
cell has a structure that does not use hydrogen and is directly fed with
fuel to generate electrical energy through an electrochemical reaction
between hydrogen contained in the fuel and an oxidizing agent being
separately supplied.

[0009] In such a fuel cell, a stack is configured as several to tens of
unit cells each consisting of a membrane electrode assembly (MEA) and a
separator.

[0010] The membrane electrode assembly includes a polymer electrolyte
membrane, a pair of catalyst layers installed on both faces of the
polymer electrolyte membrane, and a gas diffusion layer (GDS) installed
on each of the catalyst layers.

[0011] However, it is difficult to avoid the gas diffusion layer affecting
the catalyst layer when being installed on the catalyst layer. That is,
it is not desirable to directly attach the gas diffusion layer to the
catalyst layer.

[0012] Therefore, a stack is typically assembled by disposing a pair of
gas diffusion layers on both sides of a membrane electrode assembly in a
separated state and firmly attaching a separator to the outside of the
gas diffusion layers. This causes a process of assembling stacks to be
difficult.

[0013] The above information disclosed in this Background section is only
for enhancement of understanding of the background of the described
technology and therefore it may contain information that does not form
the prior art that is already known in this country to a person of
ordinary skill in the art.

SUMMARY

[0014] According to an aspect of embodiments of the present invention, a
membrane electrode assembly and a fuel cell stack have improved adhesion
between an electrolyte membrane and a gas diffusion layer, thereby
facilitating a stack assembly process.

[0015] According to an exemplary embodiment of the present invention, a
membrane electrode assembly includes: an electrolyte membrane; a catalyst
layer on the electrolyte membrane; a gas diffusion layer attached to the
catalyst layer; and an adhesive layer between the electrolyte membrane
and the gas diffusion layer around an outer edge of the catalyst layer.

[0016] The adhesive layer may be on at least one of the electrolyte
membrane or the gas diffusion layer facing each other, and bond the
electrolyte membrane and the gas diffusion layer to each other.

[0017] An inner edge of the adhesive layer may be spaced apart from the
outer edge of the catalyst layer.

[0018] The adhesive layer may be arranged as a closed curved line around
the outer edge of the catalyst layer.

[0019] The membrane electrode assembly may further include an edge
protection layer on an outer portion of the electrolyte membrane along
the outer edge of the catalyst layer.

[0020] The adhesive layer may be on at least one of the edge protection
layer or the gas diffusion layer facing each other, and bond the edge
protection layer and the gas diffusion layer to each other.

[0021] An inner edge of the adhesive layer may be spaced apart from a
boundary line between the edge protection layer and the catalyst layer.

[0022] The adhesive layer may be arranged as a closed curved line along
the edge protection layer.

[0023] The adhesive layer may be heat-treated in a vacuum or atmosphere.

[0024] The adhesive layer may be heat-treated with ultraviolet rays,
electron beams, or visible rays.

[0025] The adhesive layer may include at least one of epoxy, urethane,
silicon, or acryl.

[0026] According to another embodiment of the present invention, a fuel
cell stack includes: a plurality of unit cells, each including a membrane
electrode assembly and separators attached to both sides of the membrane
electrode assembly, respectively; and a pressure plate supporting and
applying pressure to the plurality of unit cells, and the membrane
electrode assembly includes an electrolyte membrane; a catalyst layer on
the electrolyte membrane; a gas diffusion layer attached to the catalyst
layer; and an adhesive layer between the electrolyte membrane and the gas
diffusion layer around an outer edge of the catalyst layer.

[0027] The adhesive layer may be on at least one of the electrolyte
membrane or the gas diffusion layer and bond the electrolyte membrane and
the gas diffusion layer to each other.

[0028] The fuel cell stack may further include an edge protection layer on
an outer portion of the electrolyte membrane along the outer edge of the
catalyst layer.

[0029] The adhesive layer may be on at least one of the edge protection
layer or the gas diffusion layer facing each other, and bond the edge
protection layer and the gas diffusion layer to each other.

[0030] According to an aspect of embodiments of the present invention, an
adhesive layer is disposed at the outer edge of a catalyst layer to be
interposed between an electrolyte membrane and a gas diffusion layer, and
bonds the gas diffusion layer to the electrolyte membrane, thus
facilitating a stack assembly process.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The accompanying drawings, together with the specification,
illustrate some exemplary embodiments of the present invention, and,
together with the description, serve to explain aspects and principles of
the present invention.

[0032] FIG. 1 is a partially exploded perspective view of a fuel cell
stack according to an exemplary embodiment of the present invention.

[0033]FIG. 2 is an exploded perspective view of a unit cell of the fuel
cell stack of FIG. 1.

[0034]FIG. 3 is a cross-sectional view of a membrane electrode assembly
of the unit cell of FIG. 2.

[0040] The present invention is described more fully hereinafter with
reference to the accompanying drawings, in which some exemplary
embodiments of the present invention are shown. As those skilled in the
art would realize, the described embodiments may be modified in various
different ways, all without departing from the spirit or scope of the
present invention. Accordingly, the drawings and description are to be
regarded as illustrative in nature and not restrictive. Like reference
numerals designate like elements throughout the specification.

[0041] FIG. 1 is a partially exploded perspective view of a fuel cell
stack 100 according to an exemplary embodiment of the present invention,
and FIG. 2 is an exploded perspective view of a unit cell 10 of the fuel
cell stack 100.

[0042] Referring to FIG. 1 and FIG. 2, the fuel cell stack 100 according
to an exemplary embodiment of the present invention includes a plurality
of unit cells 10 generating electrical energy through an electrochemical
reaction between an oxidizing agent and fuel. That is, the fuel cell
stack 100 is formed as an assembly by successively disposing a plurality
of unit cells 10.

[0044] In one embodiment, the fuel cell stack 100 may utilize pure
hydrogen or hydrogen reformed from gaseous or liquid fuel through a
typical reformer.

[0045] In one embodiment, the fuel cell stack 100 may be configured as a
polymer electrode membrane fuel cell generating electrical energy through
a reaction between an oxidizing agent and the fuel by the unit cells 10.

[0046] The fuel cell stack 100 according to an embodiment of the present
invention may be configured as a direct oxidation fuel cell generating
electrical energy through a direct reaction between an oxidizing agent
and the gaseous or liquid fuel by the unit cells 10.

[0047] The fuel cell stack 100 according to an embodiment of the present
invention may utilize pure oxygen stored in a separate storage unit as
the oxidizing agent reacting with the fuel, or may utilize air containing
oxygen.

[0048] In the fuel cell stack 100 according to an embodiment of the
present invention, each of the unit cells 10 has a membrane electrode
assembly (MEA) 20 at a center region, and separators 13 and 15
respectively disposed on both faces of the membrane electrode assembly 20
to be attached (e.g., pressed) together.

[0049] The fuel cell stack 100 may include pressure plates 31 and 32
respectively disposed at the outermost sides in a direction in which the
unit cells 10 are stacked, such that the plurality of unit cells 10 are
firmly attached, or pressed, to each other. However, the present
invention is not limited thereto.

[0050] For example, in another embodiment, the fuel cell stack may exclude
the pressure plates and may instead include separators located at the
outermost sides of the plurality of unit cells, so as to function as the
pressure plates (this is not illustrated in the accompanying drawings).

[0051] The separators 13 and 15 are firmly attached to both sides of the
membrane electrode assembly 20 with the membrane electrode assembly 20
interposed therebetween, and have fuel passages 13a and oxidizing-agent
passages 15a at both sides of the membrane electrode assembly 20,
respectively.

[0052] The fuel passages 13a of the separator 13 on one side are
positioned at the side of an anode of the membrane electrode assembly 20,
which will be described later, and the oxidizing-agent passages 15a on
the other side are positioned at the side of a cathode of the membrane
electrode assembly 20.

[0053] In one embodiment, the fuel passages 13a and the oxidizing-agent
passages 15a are linearly disposed in the respective separators 13 and 15
at intervals (e.g., at predetermined intervals). In one embodiment, the
fuel passages 13a are alternately connected at both ends in a generally
zigzag configuration, and the oxidizing-agent passages 15a are also
alternately connected at both ends in a generally zigzag configuration.
Of course, the structures of the fuel passages 13a and the
oxidizing-agent passages 15a are not limited thereto and, in other
embodiments, may have any other suitable structures.

[0054] The membrane electrode assembly 20 includes an active area 201 in
which an electrochemical reaction takes place, and an inactive area 202
which is adjacent to an edge of the active area 201. The inactive area
202 may be provided with a gasket (not shown) sealing the edges of the
closely located faces of the separators 13 and 15 corresponding to the
active area 201.

[0055]FIG. 3 is a cross-sectional view of the membrane electrode assembly
20 of the unit cell 10, and FIG. 4 is a cross-sectional view of the unit
cell 10 of the fuel cell stack 100.

[0056] Referring to FIGS. 3 and 4, the membrane electrode assembly 20 has
an electrolyte membrane 21 at a center region, and an anode 40 and a
cathode 50 disposed on both faces of the electrolyte membrane 21,
respectively.

[0057] In one embodiment, the electrolyte membrane 21 is formed of a solid
polymer electrolyte with a thickness of between 5 μm and 200 μm,
thus enabling ion exchange that moves protons generated in an anode
catalyst layer 42 to a cathode catalyst layer 52.

[0058] The anode 40 forming one face of the membrane electrode assembly 20
is a portion that is fed with a fuel gas through the fuel passages 13a
disposed between the separator 13 and the membrane electrode assembly 20.
The anode 40 includes the anode catalyst layer 42 and an anode gas
diffusion layer 41.

[0059] The anode gas diffusion layer 41 includes an anode microporous
layer (MPS) (not shown) formed on the anode catalyst layer 42, and an
anode backing layer (not shown) formed on the anode microporous layer.
The fuel gas is dispersed as passing through the microporous layer and
delivered into the anode catalyst layer 42.

[0060] The cathode 50 forming the other face of the membrane electrode
assembly 20 is a portion that is fed with an oxidizing-agent gas through
the oxidizing-agent passages 15a disposed between the separator 15 and
the membrane electrode assembly 20. The cathode 50 includes the cathode
catalyst layer 52 and a cathode gas diffusion layer 51.

[0061] The cathode gas diffusion layer 51 includes a cathode microporous
layer (not shown) formed on the cathode catalyst layer 52, and a cathode
backing layer (not shown) formed on the cathode microporous layer. The
oxidizing-agent gas is dispersed as passing through the cathode
microporous layer and delivered into the cathode catalyst layer 52.

[0062] In one embodiment, the membrane electrode assembly 20 includes an
anode adhesive layer 43 disposed at an outer edge of the anode catalyst
layer 42, and a cathode adhesive layer 53 disposed at an outer edge of
the cathode catalyst layer 52.

[0063] The anode adhesive layer 43 is disposed on a surface of the
electrolyte membrane 21 at the outer edge of the anode catalyst layer 42.
The anode adhesive layer 43 bonds together the electrolyte membrane 21
and the anode gas diffusion layer 41 at the outer edge of the anode
catalyst layer 42.

[0064] The cathode adhesive layer 53 is disposed on another surface of the
electrolyte membrane 21 at the outer edge of the cathode catalyst layer
52.

[0065] The cathode adhesive layer 53 bonds together the electrolyte
membrane 21 and the cathode gas diffusion layer 51 at the outer edge of
the cathode catalyst layer 52.

[0066] In one embodiment, the anode adhesive layer 43 is provided on the
electrolyte membrane 21 so as to bond together the electrolyte membrane
21 and the anode gas diffusion layer 41 facing each other. In other
embodiments (not shown), the anode adhesive layer 43 may be provided on
the anode gas diffusion layer 41, or on both faces of the electrolyte
membrane 21 and the anode gas diffusion layer 41 facing each other.

[0067] Since the anode adhesive layer 43 is disposed at the outer edge of
the anode catalyst layer 42, the anode adhesive layer 43 can bond the
anode gas diffusion layer 41 and the electrolyte membrane 21 to each
other without interrupting the activation of the anode catalyst layer 42.

[0068] In one embodiment, the outer edge of the anode catalyst layer 42
and an inner edge of the anode adhesive layer 43 are spaced apart from
each other by a first interval G1. The first interval G1 contributes to
preventing or substantially preventing the activation of the anode
catalyst layer 42 adjacent to the anode adhesive layer 43 from being
interrupted by the anode adhesive layer 43.

[0069] In one embodiment, the cathode adhesive layer 53 is provided on the
electrolyte membrane 21 so as to bond together the electrolyte membrane
21 and the cathode gas diffusion layer 51 facing each other. In other
embodiments (not shown), the cathode adhesive layer 53 may be provided on
the cathode gas diffusion layer 51, or on both faces of the electrolyte
membrane 21 and the cathode gas diffusion layer 51 facing each other.

[0070] Since the cathode adhesive layer 53 is provided at the outer edge
of the cathode catalyst layer 52, the cathode adhesive layer 53 can bond
the electrolyte membrane 21 and the cathode gas diffusion layer 51 to
each other without interrupting the activation of the cathode catalyst
layer 52.

[0071] In one embodiment, an inner edge of the cathode adhesive layer 53
and the outer edge of the cathode catalyst layer 52 are spaced apart from
each other by a second interval G2. The second interval G2 contributes to
preventing or substantially preventing the activation of the cathode
catalyst layer 52 adjacent to the cathode adhesive layer 53 from being
interrupted by the cathode adhesive layer 53.

[0072] Referring to FIG. 5, in one embodiment, the anode adhesive layer 43
is formed as a closed curved line along the outer edge of the anode
catalyst layer 42. Accordingly, the anode adhesive layer 43 provides a
stable structure for bonding the anode gas diffusion layer 41 and the
electrolyte membrane 21 together.

[0073] In one embodiment, the cathode adhesive layer 53 is formed as a
closed curved line (not shown) along the outer edge of the cathode
catalyst layer 52. Accordingly, the cathode adhesive layer 53 provides a
stable structure for bonding the cathode gas diffusion layer 51 and the
electrolyte membrane 21 together.

[0074] The anode adhesive layer 43 and the cathode adhesive layer 53 are
bonded to the electrolyte membrane 21 by pressing the anode gas diffusion
layer 41 and the cathode gas diffusion layer 51, respectively, as
indicated by the arrows shown in FIG. 3. In one embodiment, the anode
adhesive layer 43 and the cathode adhesive layer 53 may then be subjected
to a heat treatment in a vacuum or atmosphere. In one embodiment, the
anode adhesive layer 43 and the cathode adhesive layer 53 may be
heat-treated with ultraviolet rays, electron beams, or visible rays.

[0075] In one embodiment, the anode adhesive layer 43 and the cathode
adhesive layer 53 may be formed using at least one of epoxy, urethane,
silicon, or acryl.

[0076] As described above, according to an exemplary embodiment of the
present invention, the anode adhesive layer 43 and the cathode adhesive
layer 53 are directly formed on the electrolyte membrane 21, bonding the
anode gas diffusion layer 41 directly to the anode adhesive layer 43, and
bonding the cathode gas diffusion layer 51 directly to the cathode
adhesive layer 53.

[0077] Hereinafter, another exemplary embodiment will be described. In the
following description, description of components and configurations which
are the same as those described above is omitted, and only the
differences will be described.

[0078]FIG. 6 is a cross-sectional view of a membrane electrode assembly
70 of a unit cell 60 of a fuel cell stack according to another exemplary
embodiment of the present invention, and FIG. 7 is a cross-sectional view
of the unit cell 60 of a fuel cell stack including the membrane electrode
assembly 70.

[0079] Referring to FIG. 6 and FIG. 7, unlike the membrane electrode
assembly 20 described above, the membrane electrode assembly 70 has an
anode edge protection layer 44 and a cathode edge protection layer 54
attached to the edges, or outer portions, of both faces of the
electrolyte membrane 21 along the outer edges of the anode catalyst layer
42 and the cathode catalyst layer 52, respectively.

[0080] An anode adhesive layer 83 can bond protons together interposed
between the anode edge protection layer 44 and the anode gas diffusion
layer 41 at the outer edge of the anode catalyst layer 42. A cathode
adhesive layer 93 can bond protons together interposed between the
cathode edge protection layer 54 and the cathode gas diffusion layer 51
at the outer edge of the cathode catalyst layer 52.

[0081] In one embodiment, the anode adhesive layer 83 is provided on the
anode edge protection layer 44 and the anode gas diffusion layer 41
facing each other to be bonded to each other, such that the anode gas
diffusion layer 41 is attached to the anode edge protection layer 44 and
the electrolyte membrane 21.

[0082] Since the anode adhesive layer 83 is provided at the outer edge of
the anode catalyst layer 42, the anode adhesive layer 83 can bond the
anode edge protection layer 44 and the anode gas diffusion layer 41 to
each other without interrupting the activation of the anode catalyst
layer 42.

[0083] The inner edge of the anode adhesive layer 83, in one embodiment,
is spaced apart by a first interval G21 from a boundary line between the
anode edge protection layer 44 and the anode catalyst layer 42. The first
interval G21 contributes to preventing or substantially preventing the
activation of the anode catalyst layer 42 adjacent to the anode adhesive
layer 83 from being interrupted by the anode adhesive layer 83.

[0084] The anode edge protection layer 44 prevents or substantially
prevents the anode gas diffusion layer 41 from trespassing between the
anode catalyst layer 42 and the electrolyte membrane 21, thus preventing
or substantially preventing deterioration of the electrolyte membrane 21
caused by contact between the anode gas diffusion layer 41 and the
electrolyte membrane 21. Accordingly, a pin hole of the electrolyte
membrane 21 caused by the deterioration may be avoided.

[0085] In one embodiment, the cathode adhesive layer 93 is provided on the
cathode edge protection layer 54 and the cathode gas diffusion layer 51
facing each other to be bonded together, thus attaching the cathode gas
diffusion layer 51 to the cathode edge protection layer 54 and the
electrolyte membrane 21.

[0086] Since the cathode adhesive layer 93 is provided at the outer edge
of the cathode catalyst layer 52, the cathode adhesive layer 93 can bond
the cathode edge protection layer 54 and the cathode gas diffusion layer
51 to each other without interrupting the activation of the cathode
catalyst layer 52.

[0087] The inner edge of the cathode adhesive layer 93, in one embodiment,
is spaced apart by a second interval G22 from a boundary line between the
cathode edge protection layer 54 and the cathode catalyst layer 52. The
second interval G22 contributes to preventing or substantially preventing
the activation of the cathode catalyst layer 52 adjacent to the cathode
adhesive layer 93 from being interrupted by the cathode adhesive layer
93.

[0088] The cathode edge protection layer 54 prevents or substantially
prevents the cathode gas diffusion layer 51 from trespassing between the
cathode catalyst layer 52 and the electrolyte membrane 21, thus
preventing or substantially preventing deterioration of the electrolyte
membrane 21 caused by contact between the cathode gas diffusion layer 51
and the electrolyte membrane 21. Accordingly, a pin hole of the
electrolyte membrane 21 caused by the deterioration may be avoided.

[0090] In one embodiment, the cathode adhesive layer 93 is formed as a
closed curved line (not shown) along the cathode edge protection layer 54
and thus provides a stable structure for bonding the cathode gas
diffusion layer 51 and the cathode edge protection layer 54.

[0091] While the present invention has been described in connection with
certain exemplary embodiments, it is to be understood that the invention
is not limited to the disclosed embodiments, but, on the contrary, is
intended to cover various modifications and equivalent arrangements
included within the spirit and scope of the appended claims, and
equivalents thereof.